The Kamen Riders, known as Oni, fight Makamou, man eating beasts with "pure sound". They have been around for hundreds of years, protecting humans and fighting against the Makamou. One of the Oni, a man named Hibiki has a teacher and apprentice-like relationship with Asumu Adachi. A young boy unsure of himself and is at a crossroads in his life as he transitions to high school, Asumu learns to be an adult through watching Hibiki and the other Oni as they all train together to hone their skills in fighting the Makamou and the homunculi aiding them. However, the sudden raise of Makamou numbers proves to be a prelude to an upcoming calamity.

Kogure reveals his training is meant to allow Hibiki to wield the Armed Saber, a weapon that will allows him to become even more powerful than his Kurenai form. During a battle later on, Todoroki uses the Armed Saber and is sent flying by its power. In an act of desperation, Hibiki attempts to use the saber, only to meet the same result as Todoroki. The two Oni then lose the ability to transform. In the past when this has happened, Oni were unable to ever regain their powers, but as Danki and Shouki revealed, when Kogure used them as his guinea pigs, if an Oni is put through intense training, their powers will eventually return. Danki and Shouki regain their powers after a month of training, a time frame that Hibiki needed to beat. Through his training with Kogure, Hibiki, along with Todoroki, regain their powers. In the next battle after regaining their powers, Hibiki and Todoroki are pit against one of the strongest known Makamou. Kogure appears and throws Hibiki the Armed Saber, telling him that it was always destined to be used by him and that it will unlock his true power. A hesitant Hibiki finally uses the saber and easily defeats the Makamou. Hibiki meets another boy named named Kyosuke, who was estranged from his father and when he met Hibiki, he began pursuing him to allow him to be his student.

Only knowing of what his father had done in life, Kyosuke saw becoming an Oni as his chance to be greater than his father. Hibiki claimed this was a selfish reason for wanting to be an Oni and would not allow him to become his student, but Kyosuke was adamant about becoming his student. Eventually Kyosuke's rivalry with Asumu became a partnership as the two began pledging to Hibiki to allow them to become his students. Unsure of his skills as a teacher and not wanting to lose another student as he once did, Hibiki denies every plea they make. Later on when Akira Amami gives up being a student of Ibuki, she persuades Hibiki to let Asumu and Kyosuke become his students. Under Hibiki, Asumu was the better student with Kyosuke struggling in nearly every training session. Hibiki talks Asumu into him continuing to be his student. For a while longer, the three continue their training before Hibiki finally realizes that Asumu's place in this world is not as an Oni. He allows Asumu to quit but feels great regret for being the one to push him to stay his student. Following the great battle against the Makamou in the "Orochi sealing", Hibiki and Asumu lost touch and meet each other at a hospital that Asumu works at a year later. Hibiki says that even though he can't be Asumu's mentor as an Oni, he can be his mentor in life and help him be a better person. The two watch a sunrise as they remember their first meeting and Hibiki reveals to Asumu that he was his apprentice from the start, with Asumu agreeing to stay by Hibiki's side despite choosing not to become an Oni himself.